#17,235
Every once in a while an event occurs that is so momentous that it changes the world for generations, perhaps forever. Our entering the atomic era at the end of World War II is perhaps the most obvious example.
While it has spurred an era of great scientific discovery, it also immediately led to a `cold war' and huge commitments to national defense, which continue to this day.
Once that `genie' was out of the bottle, there was no going back, and subsequent generations have had to live under the specter of potential nuclear accidents, `dirty' bombs, and even full out nuclear war.
We've managed to avoid most of those pitfalls, but not without considerable cost.
In many ways, the emergence of COVID carries some of these same attributes, and while its impacts going forward are uncertain, they could persist for years - even decades - to come.
The SARS-CoV-2 virus is now ubiquitous in humans - and given its penchant for reinventing itself - is likely to remain so for quite some time.
While the Omicron virus produces less severe illness than its predecessor - due in part to acquired immunity from previous exposures and vaccines - there are no guarantees that future variants will follow this pattern.
The wild card in all of this is, increasingly, SARS-CoV-2 is spilling over from humans to other species. And as we've already seen, that can lead to new, potentially dangerous variants, that can spill back into humans.
- In the fall of 2020 SARS-CoV-2 jumped from humans to farmed mink in Denmark, and began to mutate into new mink-variants (see Denmark Orders Culling Of All Mink Following Discovery Of Mutated Coronavirus). As a result, several mutated viruses jumped back into humans (see WHO 2nd Update: SARS-CoV-2 mink-associated variant strain – Denmark).
- Since then, we've seen similar events in the United States (see CDC: Investigating Possible Mink-To-Human Transmission Of SARS-CoV-2 In The United States) and in Hong Kong (see Hong Kong Detects COVID In Pet Store Hamsters - Suspends Sales & Orders Cull).
- Last November, in Preprint: SARS-CoV-2 Exposure in Norwegian rats (Rattus norvegicus) from New York City we looked at a report that found a relatively high percentage of rats tested had been exposed to the coronavirus, and found that both Delta and Omicron variants can also cause robust infections in Sprague Dawley® rats.
- Also last November, in Nature: Divergent SARS-CoV-2 Variant Emerges in White-tailed Deer with Deer-to-Human Transmission (Revisited), we looked at a study that found that the virus was following ` a distinctive evolutionary trajectory in deer'.
- And last spring, we saw evidence of suspected transmission of COVID from a companion animal to a human (see EID Journal: Suspected Cat-to-Human Transmission of SARS-CoV-2 - Thailand).
- While controversial, there is even some evidence to suggest that the Omicron variant may have evolved after the virus jumped to mice or other rodents (see Evidence for a mouse origin of the SARS-CoV-2 Omicron variant), and then spilled back into humans (for more, see Maryn McKenna's Wired article Where Did Omicron Come From? Maybe Its First Host Was Mice).
We've seen other reports - including CCDC Weekly Perspectives: COVID-19 Expands Its Territories from Humans to Animals from China - which warn that the spillover of COVID into other species provides the virus with new opportunities to evolve, adapt, and potentially return with a vengeance.
Ecology of SARS-CoV-2 in the post-pandemic era
Yafei Meng, David M Irwin, Yongyi Shen
Open Access Published:December 21, 2022
DOI:https://doi.org/10.1016/S2666-5247(22)00361-5
The outbreak of COVID-19, caused by SARS-CoV-2, has posed a severe threat to global public health. The omicron variant is less pathogenic and causes more asymptomatic infections, thus the emergency phase might have passed. Many governments are rolling back restrictions, and, as of Dec 19, 2022, there are 153 countries without any travel restrictions (data from Travel Off Path). However, the omicron variant shows a greater propensity for human-to-human transmission than previous variants and the wild-type strain. Furthermore, the incidence of infection is still high (7·9–18·9%) in humans who received the two RNA vaccines (BNT162b2 and mRNA-1273) or were naturally infected.1 It seems that the disease will become endemic and will be characterised by a lower pathogenicity, but with higher transmission rates, leading to large infection and reinfection numbers in the post-pandemic era (endemic phase). The ecology of SARS-CoV-2 in the post-pandemic era needs attention.
SARS-CoV-2 transmission and reverse transmission from humans to animals that are in close contact with humans, such as zoo animals (pumas, tigers, lions, and gorillas), fur-bearing animals (minks and ferrets), and pets (cats and dogs) has been widely reported.2, 3 The pet population is very large in industrialised nations, where a high proportion of households have pets. For example, 25·4% of households in the USA have cats (data from the American Veterinary Medical Association). Considering the intimate contact between pets and zoo animals with humans, especially the large number of pets, the circulation of SARS-CoV-2 in these animals should not be neglected (appendix).
ACE2 is the receptor for SARS-CoV-2. Within carnivores, a very limited number of amino acid differences are present in the ACE2 protein sequence at key sites involved in its interaction with the SARS-CoV-2 spike protein (appendix). This suggests that other carnivores genetically related to cats, dogs, minks, and ferrets are also likely to be susceptible to SARS-CoV-2. Many small and medium-sized carnivores, such as foxes, coyotes, weasels, skunks, badgers, and raccoons, have successfully colonised urban and suburban areas, where they exhibit population densities higher than in rural and wild environments.4
Their food resources include human refuse, synanthropic rodents and birds, pets, and livestock. These urban wild carnivores might form a bridge for the transmission of viruses between pets and other animals in the wild. Indeed, some wild animals, such as white-tailed deer, are sensitive to SARS-CoV-2.5 The interactions between humans, their pets, and urban wildlife increase the risk of potential expansions of SARS-CoV-2 in other species of wildlife.These urban wild carnivores might form a bridge for the transmission of viruses between pets and other animals in the wild.
The above discussion suggests that the ecology of SARS-CoV-2 could be more complex than for other zoonotic viruses (appendix). Infections in humans would facilitate frequent human–animal transmissions. Then, the virus could experience sustained evolution with adaptation to multiple species of animals that results in antigenicity changes before subsequent reverse transmission to humans. This would make disease control more difficult. Therefore, characterisation of SARS-CoV-2 ecology and greater levels of surveillance for infections in animals, especially pets, zoo animals, and urban and suburban wildlife, are imperative in the post-pandemic era.
It's been estimated that the risk of seeing a severe pandemic in any given year is about 2%, but that number was based largely on influenza A being the primary pandemic threat. Now that the SARS-CoV-2 virus is well established, that number will likely increase.
In 2021, in PNAS Research: Intensity and Frequency of Extreme Novel Epidemics, researchers suggested that the probability of novel disease outbreaks will likely grow three-fold in the next few decades. While that seems reasonable to me, only time will tell.How much? I'm no expert, but others have weighed in.
Having lived through 4 declared pandemics (1957, 1968, 2009, 2000), one pseudo-pandemic (1977 `Russian flu'), and numerous close calls (H7N9, SARS-CoV, Ebola in West Africa, MERS-CoV, etc.) it is hard to envision a world where these sorts of events happen 3 times more often.
